Field of the Invention
The present invention relates to a method for preparing high voltage direct current (HVDC) cable sections and accessories.
Discussion of Related Art
It is well known that accessories in a cable system, such as joints and terminations, form discontinuities in the outer screen. As the cables' concentric geometry is disrupted this allows for electric field enhancement that may be strong enough to break down the insulation at this area. Electrical breakdowns, when a cable system is subjected to DC fields and elevated temperatures tend to appear in the outer periphery of the cable insulation due to the field inversion which inverts the peak field from the inner periphery of the cable insulation.
At high voltages these effects are even more demanding on the insulation.
The term high voltage refers to voltages of above 45 kV and ranging up to 800 kV.
An HVDC cable comprises at least an electrical conductor surrounded by at least one first semiconducting layer, an electrically insulating layer surrounding the first semiconducting layer and a second semiconducting layer surrounding the insulating layer, optionally one or more further layers surround the second semiconducting layer. When an end of an HVDC cable is prepared for termination or jointing with another cable the one or more further layers and the second semiconducting layer is removed from an end section of the cable to provide for termination and/or jointing of the different elements of the cable. It is especially within this end section no longer surrounded by a second semiconducting layer that electrical breakdowns have been observed.